Naphthocyclobutenes and Benzodicyclobutadienes: Synthesis in the Solid State and Anomalies in the Bond Lengths

The title four-membered ring compounds, naphthocyclobutenes and benzodicyclobutadienes, were produced by thermal cyclization reaction of crystalline 1,2-diallenylbenzenes and 1,6-diethynyldiallenes, respectively. These solid-state reactions proceeded efficiently and stereoselectively. The naphthocyclobutenes were shown to have extremely long C-C bonds (1.720−1.733 Å). The benzodicyclobutadienes were also shown to have extremely long C-C bonds (1.540 Å).